This invention relates to devices for measuring the relative position of a moving frame of reference, and more particularly to an optically phase conjugated light system which may be used as a relative position sensor.
The measurement of changes in the relative position of a closed system such as an aircraft has posed a challenge in the past, since the ground cannot be used as a direct reference to obtain position updates. A common approach has been to provide an accelerometer, which detects any positive or negative acceleration of the body, and to integrate the measured acceleration values to obtain velocity and position information.
The accelerometers generally used are electromechanical transducers which produce a voltage proportional to, and in synchronism with, the time rate of change of the velocity of a body. One common form of accelerometer, for example, employs a piezoelectric ceramic-disc array provided with plated metallic surfaces cemented between a small mass and a base. The base is secured to the body whose acceleration is being measured, and the acceleration of the body causes a force to be applied by the mass to the ceramic-disc array. This force produces an output voltage between the plated metallic surfaces which provides an indication of the body's acceleration.
While the above type of relative position sensor has generally been satisfactory, it would be desirable to eliminate some of the mechanical aspects of the accelerometer device in order to increase the accuracy and sensitivity of the relative position sensor. It would also be desirable to measure relative position changes directly, rather than by twice integrating an acceleration signal.